1. Field of the Invention
The present invention relates to a gear-shifting apparatus for a bicycle, and to a bicycle incorporating the apparatus. More particularly, the invention relates to a gear-shifting apparatus of a type using a chain, which shifts the chain from one sprocket to another.
2. Background
One example of a known gear-shifting apparatus for a bicycle is disclosed in Japanese Patent Laid-open Official Gazette No. 2004-155280, and this known system includes: a drive sprocket connected to a crankshaft through a one-directional clutch, while the drive sprocket is being driven. The known gear-shifting apparatus of this reference also includes a sprocket cluster constituted of a plurality of gear-shifting sprockets, which is connected to an output axle for driving a rear wheel, a chain hooked to the drive sprocket and one of the gear-shifting sprockets, and a gear-shifting mechanism. The gear-shifting mechanism includes a derailer arm for rotatably supporting a guide pulley for guiding the chain to a selected gear-shifting sprocket and an arm for rotatably supporting a tension pulley for applying a tension force to the chain. When the guide pulley and the tension pulley move in the center axis direction of a derailer axle, the chain is shifted from a current gear-shifting sprocket to the selected gear-shifting sprocket. In this way, a gear-shifting operation is done.
It would be advantageous if gear-shifting operations could be done no matter what condition the bicycle travels in. For example, it is desirable to perform a gear-shifting operation quickly through a forward rotation of the crankshaft even while a bicycle moves backward in a condition where the rider is off the bicycle, or even while the bicycle is stopped. This feature would contribute to improving the performance in operating the bicycle. Particularly during bicycle racing, where racers compete in time trials, providing a racer with more opportunities for operating the gear shift will lead to better race results.
However, when the gear-shifting sprockets are not rotating forward, including a case where the gear-shifting sprockets are rotating backwards while the bicycle is moving backwards and a case where the gear-shifting sprockets are halted while the bicycle is in a stop, if a gear-shifting operation were performed so that the guide pulley moves towards the center axis direction (hereinafter referred to as the “axis direction”), a part of the chain which is hooked to the guide pulley moves in the axis direction along with the guide pulley. By contrast, a part of the chain which is hooked to one of the gear-shifting sprockets does not move in the axis direction. For this reason, the part of the chain which is hooked to the guide pulley may come off, or become derailed from, the guide pulley in some cases. If the crankshaft were caused to rotate forward while the chain is in such a condition so that the drive sprocket and the gear-shifting sprockets rotate forward, the derailed part of the chain may get stuck between the guide pulley and the derailer arm in some cases. In other cases, the derailed part of the chain may be positioned beside the guide pulley and inwards in the radial direction from the outermost peripheral end of the guide pulley. This makes it difficult for the derailed part of the chain to re-engage with the guide pulley.
In addition, while the gear-shifting sprockets are rotating backwards, if a speed at which the gear-shifting sprockets are rotating is high, or if an equivalent occurs, a part of the chain may stagnate between the guide pulley and one of the gear sifting sprockets. If a part of the chain stagnates in this manner, the chain comes off the guide pulley more easily.
Furthermore, when the derailed part is in the process of engaging with the guide pulley again, if an obstacle hinders the derailed part from moving in a pathway where the derailed part is going to move, for example if there was a step made of a protrusion jutting out from the pathway where the derailed part is going to move, the promptness with which the derailed part of the chain returns to an engaged state with the guide pulley is decreased. In addition, the reliability with which the derailed part is caused to engage with the guide pulley again is reduced.
Still furthermore, if a gear-shifting operation is performed during a halt of the gear-shifting sprockets while the bicycle is in a stop or in an equivalent condition, the chain may come off the tension pulley at a part of the tension pulley which leads in the chain because of the following mechanism. When the gear-shifting operation moves the guide pulley and the tension pulley in the center axis direction (hereinafter referred to as an “axis direction”), a part of the chain which is currently on the top of the tension pulley moves along with the tension pulley in the axis direction on a part of the tension pulley which leads in the chain. By contrast, a part of the chain which is currently on the top of the drive sprocket hardly moves in the axis direction. Moreover, the chain is halted. In this manner, the chain comes off from the tension pulley. If a crankshaft were caused to make a forward rotation, and if accordingly the drive sprocket and the gear-shifting sprockets made a forward rotation while they are in such a condition, this derailed part of the chain which has come off from the tension pulley gets stuck between the tension pulley and the arm in some cases. In other cases, the derailed part gets stuck between the side of the tension pulley and a part inwards in the axis direction from the outermost side end of the tension pulley. In these cases, it is difficult for the derailed part to re-engage with the tension pulley.
With the aforementioned matters taken into consideration, the present invention has been made.
An object of the present invention is to provide a gear-shifting apparatus which makes it easier for the derailed part of the chain to return to an engaged state with the guide pulley even when the chain comes off from the orbital plane of the guide pulley due to a gear-shifting operation, and which enables a gear-shifting operation to be performed even when the gear-shifting sprockets are not rotating forward, including a case where the gear-shifting sprockets are rotating backwards.
A further object of the present invention is to inhibit the number of parts in the gear-shifting apparatus from increasing due to providing engagement recovery means to the gear-shifting apparatus, and is to reduce costs for the gear-shifting apparatus.
A further object of the present invention is to miniaturizing the gear-shifting apparatus in the axis direction.
A further object of the present invention is to miniaturize the engagement recovery means in the axis direction, accordingly to miniaturize the gear-shifting apparatus, and to increase rigidity of the arm, which supports the tension pulley, by use of the engagement recovery means.
A further object of the present invention is to improve promptness and reliability in which the derailed part of the chain returns to an engaged state with the guide pulley.
A further object of the present invention is to intend to miniaturize the gear-shifting apparatus in the axis direction, and concurrently to enable a smooth gear-shifting to be performed.
A further object of the present invention is to provide a gear-shifting apparatus which makes it easy to cause a derailed chain to return to a condition of engaging with the tension pulley when a gear-shifting operation has got the chain off the tension pulley, and which accordingly enables a new gear-shifting to be operated while the gear-shifting sprockets are in a halt and while the gear-shifting sprockets do not make a forward rotation.
A further object of the present invention is to increase the rigidity of the arm, and concurrently to cause the derailed part of the chain to return to a condition of engaging with the tension pulley more securely.
A further object of the present invention is to cause the derailed part to return to a condition of engaging with the tension pulley more securely, and concurrently to make the derailer arm lighter in weight.
A still further object of the present invention is to enable a gear-shifting to be operated easily.
A first aspect of the present invention relates to a gear-shifting apparatus including a plurality of gear-shifting sprockets arranged in the axis direction, and a changing mechanism for changing the chain from one sprocket to another among the plurality of gear-shifting sprockets in response to a gear-shifting operation. The changing mechanism includes a pulley support member, which rotatably supports the guide pulley to which the chain is hooked, and which moves in the axis direction by means of a gear-shifting operation. With regard to the gear-shifting apparatus, the guide pulley guides the chain hooked to one sprocket which has been selected out of the plurality of gear-shifting sprockets. In the gear-shifting apparatus, the pulley support member is provided with the engagement recovery means for causing the derailed part of the chain, which has been derailed from the orbital plane of the guide pulley, to engage with the guide pulley. The engagement recovery means includes a first extending part and a second extending part. The first extending part and the second extending part are arranged leftwards and rightwards in the axis direction from the orbital plane, and extend in the axis direction and in a direction away from the orbital plane. Each of the extending parts guides the derailed part, which has gone onto the extending part, in a way that the derailed part slides on the extending part and moves towards the orbital plane due to a tension force on the chain, and thereafter engages with the guide pulley.
In the case of the gear-shifting apparatus according to the first aspect of the present invention, the first extending part and the second extending part, which constitute the engagement recovery means, guide the derailed parts of the chain respectively in a way that the derailed parts of the chain slide respectively on the first extending part and the second extending part as well as engage with the guide pulley. This occurs no matter which side in the axis direction the guide pulley moves to, even when the chain comes off from the orbital plane due to movement of the guide pulley in the axis direction through a gear-shifting operation while the gear-shifting sprockets are rotating backwards or are in a halt. For this reason, while the gear-shifting sprockets are rotating forwards, the derailed parts are prevented from getting stuck between the guide pulley and the pulley support member, or from doing an equivalent thing. This enables the chain to run. Accordingly, the chain will not get stuck between one of the gear-shifting sprockets and the guide pulley (in other words, the chain will not stagnate), even if a gear-shifting operation is performed, for example, while the gear-shifting sprockets are rotating backwards. Accordingly, the chain securely returns to an engaged state with the guide pulley when the gear-shifting sprockets rotate forward.
A gear-shifting apparatus according to a second aspect of the present invention includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the first aspect of the present invention. The pulley support member includes a holder for rotatably supporting the guide pulley, and an arm for rotatably supporting a tension pulley which is supported by the holder, and which applies a tension force to the chain. The first extending part is molded integrally with the arm. The second extending part includes a spring containing part which contains a tension spring to generate a spring force with which to push the tension pulley against the chain.
In the case of the gear-shifting apparatus according to the second aspect of the present invention, the first extending part and the second extending part are provided by use of the spring containing part which contains the arm and the tension spring which are a member to support the tension pulley. This does not require preparation of a specialized member for constituting the first extending part and the second extending part.
A gear-shifting apparatus according to a third aspect of the present invention includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the first or second aspects of the present invention. The plurality of gear-shifting sprockets are arranged sequentially in a way that a gear-shifting sprocket with a larger outer diameter comes next to a gear-shifting sprocket with a smaller outer diameter to a side in the axis direction. The first extending part and the second extending part are arranged respectively in the side from the orbital plane and in the opposite side in the axis direction. A guide surface onto which the derailed part can go in the first extending part is located in a position whose distance from the centerline of rotation of the guide pulley is smaller in comparison with a guide surface onto which the derailed part can go in the second extending part.
In the case of the gear-shifting apparatus according to the third aspect of the present invention, while the guide pulley moves towards the side, interference between the first extending part and each of the gear-shifting sprockets is eliminated. In addition, a guide pulley and each of the gear-shifting sprockets are arranged so as to be closer to each other.
A gear-shifting apparatus according to a fourth aspect of the present invention includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the second or third aspects of the present invention. The first extending part is provided so as to extend into a position which makes the first extending part seem to overlap with the tension pulley when viewed from the side. A width in the axis direction of the first extending part is almost equal to a width in the axis direction of the chain.
In the case of the gear-shifting apparatus according to the fourth aspect of the present invention, the first extending part functions as a reinforcement rib of the arm. For this reason, rigidity of the arm which supports the tension pulley is increased. In addition, a guiding function of causing the derailed part to return to an engaged state with the guide pulley is secured. Furthermore, the width in the axis direction of the first extending part is made smaller.
A gear-shifting apparatus according to a fifth aspect of the present invention includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the second aspect of the present invention. The arm includes a first arm part and a second arm part. The first arm part is arranged in the axis direction by the sides respectively of the orbital planes of the guide pulley and the tension pulley. The second arm part is arranged in the axis direction by the other sides respectively of the orbital planes of the guide pulley and the tension pulley. The first arm part is provided with the first extending part. The second arm part is provided with the spring containing part so that the spring containing part is next to the second arm part in the axis direction. The second arm part is arranged in the axis direction between the guide pulley and the spring containing part. The outermost edge of the second arm part in the radial direction is located in a position whose distance from a centerline of rotation of the guide pulley is equal or smaller in comparison with the guide surface in the spring containing part onto which the derailed part can go.
In the case of the gear-shifting apparatus according to the fifth aspect of the present invention, the derailed part is guided by the second extending part so that, without being interfered by the second arm part, the derailed part moves on the guide surface smoothly and is able to return to an engaged state with the guide pulley.
A gear-shifting apparatus according to a sixth aspect of the present invention includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the fifth aspect of the present invention. The width in the axis direction of the first extending part is almost equal to the width occupied by two of the gear-shifting sprockets which are next to each other in the axis direction. The width in the axis direction of the second extending part is larger than the width in the axis direction of the first extending part.
In the case of the gear-shifting apparatus according to the sixth aspect of the present invention, the guiding function of causing the derailed part to return to an engaged state with the guide pulley is secured by use of the first extending part and the second extending part. In addition, the width in the axis direction of the first extending part is made smaller. Furthermore, even if a width in which the derailed part moves in the axis direction is larger, the second extending part causes the derailed part to securely go onto the second extending part, and accordingly causes the derailed part to return to an engaged state with the guide pulley.
A gear-shifting apparatus according to a seventh aspect of the present invention relates to a gear-shifting apparatus configured as follows. The gear-shifting apparatus includes a plurality of gear-shifting sprockets arranged in the axis direction, and a changing mechanism for changing the chain from one sprocket to another in the plurality of gear-shifting sprockets. The changing mechanism includes an arm for rotatably supporting a tension pulley for applying a tension force to the chain. In the gear-shifting apparatus, a gear-shifting operation moves the arm in the axis direction. With regard to the arm, its part near a part of the tension pulley, which leads in the chain, is provided with an engagement recovery-guiding part for causing a derailed part of the chain, which has got off an orbital plane of the tension pulley, to engage with the tension pulley. The engagement recovery-guiding part positions the entire derailed part outwards the rotation track of the outermost side end of the tension pulley in the radius direction, and concurrently guides the derailed part in order to cause the derailed part to engage with the tension pulley after the derailed part moves towards the orbital plane by means of the tension force on the chain.
This gear-shifting apparatus causes the engagement recovery-guiding part to guide the derailed part of the chain so that the derailed part of the chain returns to a condition of engaging with the tension pulley, even if a gear-shifting operation moves the tension pulley in the axis direction and thereby the chain comes off from the orbital plane of the chain when the gear-shifting sprocket is halted or in an equivalent case. This prevents the derailed part from getting stuck between the tension pulley and the arm. This enables the chain to run.
A gear-shifting apparatus according to an eighth aspect of the present invention further includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the seventh aspect of the present invention. The changing mechanism includes a guide pulley for guiding the chain to be hooked to a working sprocket which has been selected out of the plurality of gear-shifting sprockets, and a holder which rotatably supports the guide pulley, and which can move in the axis direction along with the arm. The arm includes a pair of arm parts, one of which is arranged in one side of the tension pulley and the guide pulley in their axis directions, and the other of which is arranged in the other side of the tension pulley and the guide pulley in their axis directions. A tension-pulley-side guiding part for preventing a part of the chain which is hooked to the tension pulley from getting off the pulley and a supported part which is supported by the holder are formed in each of the arm parts. An interval in the axis direction between the two supported parts is wider than an interval in the axis direction between the tension-pulley-side guiding parts.
This gear-shifting apparatus can increase the bending rigidity of each of the supported parts, which is a part onto which a force moving the arm in the axis direction functions from the changing mechanism. In addition, since the interval in the axis direction between the tension-pulley-side guiding parts in the arm is formed so as to be narrower, the tension-pulley-side guiding parts can be arranged closer to the tension pulley. This can cause the derailed part, which is guided by the engagement recovery-guiding part, to return to a condition of securely engaging with the tension pulley.
A gear-shifting apparatus according to a ninth aspect of the present invention further includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the eighth aspect of the present invention. While a center plane is defined as including a line representing the center of rotation of the tension pulley and a line representing the center of the rotation of the guide pulley, a range where the engagement recovery-guiding part is formed in the circumferential direction is a range which makes an angle to the center plane in a direction of a forward rotation of the tension pulley from the centerline of rotation of the tension pulley equal to an angle to the center plane in a direction of a reverse rotation of the tension pulley from the centerline of rotation of the tension pulley, when viewed from the side.
This gear-shifting apparatus makes it possible to sufficiently secure the range, where the engagement recovery-guiding part is formed in the circumferential direction, along the center plane. This enables the derailed part to easily return to a condition of engaging with the tension pulley. In addition, a point in the engagement recovery-guiding part at which the derailed part applies a force when the derailed part comes into contact with the engagement recovery-guiding part can be designed to come close to the center plane. Accordingly, this force can reduce a torque which is applied to each of the arm parts. This does not require each of the arm parts to be made larger, or accordingly to be heavier in weight, for the purpose of increasing torsional rigidity of each of the arm parts.
A gear-shifting apparatus according to a tenth aspect of the present invention further includes the following configuration in addition to including the same configuration as the gear-shifting apparatus according to the seventh aspect of the present invention. The arm includes a pair of arm parts which are arranged respectively on the two sides of the tension pulley, and in which the engagement recovery-guiding parts are respectively formed. Each of the engagement recovery-guiding parts has a guide plane with which the derailed part comes into contact, and which extends in the axis direction and in a direction orthogonal to the orbital plane. A position of an end portion of the guide plane which is closest to the tension pulley in the axis direction virtually agrees with, or is aligned with, a position of the inner circumferential edge of the chain engaging with the tension pulley.
This gear-shifting apparatus causes the derailed part to run onto the guide plane easily. This causes the derailment to begin at a position of the engagement recovery-guiding part, the position being in a direction a forward rotation of the tension pulley. This relieves torsion of the chain caused due to a movement in the axis direction of the tension pulley. The relief reduces a resistance force from the chain while a gear-shifting operation is being performed.
According to a first aspect of the present invention, even when part of the chain comes off the orbital plane of the guide pulley due to a gear-shifting operation which is performed while the gear-shifting sprockets are rotating backwards, in a stop or in an equivalent condition, the first extending part and the second extending part guide the derailed part so that the derailed part engages with the guide pulley again, thus enabling the chain to run. This makes it easier to cause the derailed part to return to an engaged state with the guide pulley. Accordingly, a gear-shifting operation can be performed even when the gear-shifting sprockets are not rotating forward, including a case where the gear-shifting sprockets are rotating backwards. A gear-shifting can be carried out on the base of the gear-shifting operation thus made possible.
According to the second aspect of the invention, in addition to the above-recited effect of the first aspect of the present invention, a specialized member for providing the first extending part and the second extending part is not required. Accordingly, the number of the parts of the gear-shifting apparatus provided with the engagement recovery means is reduced, and the costs for the gear-shifting apparatus is also reduced.
According to the third aspect of the invention, in addition to the above-recited effect of any of the first or second aspects of the present invention, interference between the extending part and each of the gear-shifting sprockets in conjunction with movement of the guide pulley is eliminated. Accordingly, reliability in which a gear-shifting operation is performed is secured. In addition, the guide pulley and each of the gear-shifting sprockets are arranged so as to be closer to each other. This enables the gear-shifting apparatus to be miniaturized. Furthermore, reliability in which a gear-shifting operation is performed is improved. Additionally, this enables a gear-shifting to be carried out smoothly.
According to the fourth aspect of the invention, in addition to the above-recited effect of any of the second or third aspects of the present invention, rigidity of the arm can be increased by use of the first extending part. In addition, the first extending part is miniaturized in the axis direction. Moreover, a gear-shifting sprocket cluster and the guide pulley are arranged so as to be closer to each other in the axis direction. For this reason, the gear-shifting apparatus is miniaturized in the axis direction.
According to the fifth aspect of the present invention, in addition to the above-recited effect of the second aspect of the present invention, the derailed part is guided smoothly by the second extending part so that the derailed part returns to an engaged state with the guide pulley. Accordingly, promptness and reliability with which the derailed part returns to an engaged state with the guide pulley is improved. In addition, reliability with which a gear-shifting is carried out is improved.
According to the sixth aspect of the present invention, in addition to the above-recited effect of the fifth aspect of the present invention, the extending part is miniaturized in the axis direction. The sprocket cluster and the guide pulley are arranged so as to be closer to each other in the axis direction. Accordingly, the gear-shifting apparatus is miniaturized in the axis direction. Furthermore, the gear-shifting apparatus is miniaturized in the axis direction. In addition, reliability with which the derailed part returns to a state of the engagement is improved by the second extending part. Additionally, reliability with which a gear-shifting is carried out is improved.
According to the seventh aspect of the invention, even when part of the chain comes off the orbital plane of the tension pulley due to a gear-shifting operation which is performed while the gear-shifting sprockets are in a stop or in an equivalent condition, the engagement recovery-guiding part guides the derailed part so that the derailed part engages with the tension pulley again, thus enabling the chain to run. This makes it easy to cause the derailed part to return to a condition of engaging with the tension pulley. Accordingly, a gear-shifting operation can be performed while the gear-shifting sprockets are halted and while the gear-shifting sprockets do not make a forward rotation. A gear-shifting can be carried out on the base of the gear-shifting operation thus made possible.
According to the eighth aspect of the invention, in addition to the above-recited effect of the seventh aspect of the present invention, rigidity of the supported part on which a force functions from the changing mechanism for moving the arm in the axis direction is increased. This enables the supported part to be made lighter in weight. In addition, the derailed part is caused to return to a condition of securely engaging with the tension pulley, thus improving a degree of certainty with which the derailed part returns to the condition of engaging with the tension pulley.
According to the ninth aspect of the present invention, in addition to the above-recited effect of the eighth aspect of the present invention, the range where the engagement recovery-guiding part is formed in the circumferential direction can be secured sufficiently. This improves a degree of certainty with which the derailed part returns to the condition of engaging with the tension pulley. A force which the derailed part causes to function on the engagement recovery-guiding part can reduce a torque which is applied to each of the arm parts. This enables each of the arm parts to be made lighter in weight.
According to the tenth aspect of the invention, in addition to the above-recited effect of the ninth aspect of the present invention, torsion of the chain caused due to a movement in the axis direction of the tension pulley is relieved. This enables a gear-shifting operation to be performed more easily.
Modes for carrying out the present invention are explained below by reference to an embodiment of the present invention shown in the attached drawings. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent form the detailed description of the embodiment of the invention presented below in conjunction with the attached drawings.